Patient warming used to be about keeping patients cozy and comfortable, but today the focus is on the science and the economics behind the warmth - specifically, how active warming methods can prevent such dangerous and costly complications of hypothermia as delayed recoveries and unintended outcomes. It follows that if patient warming improves surgical outcomes and shortens postanesthesia unit (PACU) stays, patient warming also decreases facility costs and provides a safer patient environment.

As evidence about patient warming's impact on hypothermia mounts, so, too, do the methods to help you monitor, prevent and treat hypothermia. From blanket warmers to fluid warmers, circulating water mattresses to water heaters, hot-air blowers to temperature-adjustable gowns to viscoelastic warming pads, there's no shortage of choices for the OR manager to keep patients warm and comfortable before, during and after surgery. And, experts say, there's no excuse for not actively preventing hypothermia.

"You need to be actively warming your patients for almost any procedure, including shorter procedures, because science has proven that anesthesia lowers your core temperature," says Brian Stelley, senior marketing manager of Gaymar Industries. As studies have shown that all active warming methods are all useful in the prevention and treatment of hypothermia, Mr. Stelley's advice is to "pick the best product or best combination of products for that patient and for that situation."

Hypothermia: It's preventable
Inadvertent hypothermia (defined as a core temperature below 36' C [97' F]) occurs in 60 to 90 percent of post-surgical patients, according to separate studies, affecting more than 14 million patients annually. When unrecognized, the condition may lead to dangerous and costly complications. For example, inadvertent hypothermia may be associated with:

• Delayed excretion of anesthetic agents. Central nervous system depression and delay in the excretion of anesthetic drugs lead to longer anesthesia times and longer times in PACUs.
• Coagulopathy. Increased firbinolysis increases further in a cold patient, and a decline in platelet activity causes a tendency to bleed.
• Infection. Hypothermia can lead to decreased resistance to surgical wound infections.
• Cardiac events. Post-operative shivering places additional demands on the body, especially in the presence of coronary disease. The potential exists for increased incidence of cardiac events.

Hypothermia also has been associated with costly complications. It has been calculated that hypothermia averaging only 1.5' C below normal causes cumulative adverse surgical outcomes that add $2,500 to $7,000 to costs for each surgical patient.

Effects of anesthesia on thermoregulation
In the perioperative setting, anesthetic drugs can compromise patients' natural temperature-regulating mechanisms by altering one or more components of the thermoregulatory system. Because of the anesthesia, the patient is unable to restore body heat through the normal mechanisms of increased muscle activity or shivering. This inability to respond normally to changes in body temperature contributes to hypothermia.

The risks of hypothermia appear similar with regional and general anesthesia. With both types of anesthesia, the most important cause of core temperature reduction is redistribution of heat from the core to the periphery.

• General anesthesia. Within 30 minutes after induction of general anesthesia, the vasodilation induced by anesthetic agents causes redistribution of heat flow from the core to the peripheral thermal compartment. The result is a drop in core temperature.
• Regional anesthesia. With regional anesthesia, blockade of the autonomic nerve fibers in the area affected by the anesthetic block results in a redistribution of heat from the center toward the periphery through inhibition of sympathetic tonic discharge in the area.

Published research
By maintaining normothermia in all patients undergoing surgical intervention, a growing number of studies have proven that you can prevent many potential complications. Here are highlights from a few:

• A prospective, randomized, controlled study found that laparoscopic colorectal surgery results in less postoperative pain and earlier recovery of bowel function than conventional laparotomy, but does not reduce the risk for perioperative hypothermia. Accordingly, active warming must be provided to patients also during laparoscopic procedures.
  SOURCE: Anesth Analg 2002 Aug;95(2):467-71

• Warming patients before 'clean' surgery appears to aid the prevention of postoperative wound infection. This therapy has no known side effects and may provide an alternative to prophylactic antibiotics, and the associated risk of allergy and resistance, in this type of surgery.
  SOURCE: Melling, A.C., Ali, B., Scott, E.M. and Leaper, D.J.The Lancet, 2001; 358(9285): 882-886

• A comparative study of three warming interventions to determine the most effective in maintaining perioperative normothermia in patients having knee surgery found that reflective technology was less effective than using two cotton blankets, whereas active surface warming with the forced-air method most effectively maintained normothermia.
  SOURCE: Anesth Analg 2003 Jan;96(1):171-6

• A study that evaluated whether the intraoperative use of fluid-warming devices might introduce risks of their own found the use of the Hotline fluid warmer can result in infusion of air into the patient, introducing possible risk of air embolism.
  SOURCE: J Clin Monit Comput 1999 May;15(3-4):149-52

• A review of the literature on the prevention of surgical site infections published during 2001 found that "there appear to be few arguments against application of this cheap and safe measure" for reducing the rate of surgical site infections generally or locally at the incision site
  SOURCE: Curr Opin Infect Dis 2002 Aug;15(4):427-32

• A study that examined whether the Bair Hugger forced-air patient warming system during prolonged abdominal vascular surgery may lead to increased bacterial contamination of the surgical field by mobilization of the patient's skin flora found that forced-air warming does not force patients' resident skin organisms into and contaminate the operating theatre atmosphere, that such systems are unlikely to increase the incidence of wound and prosthetic infections, and that it is unlikely to affect the surgical field adversely.
  SOURCE: Augustine Medical

As you can see, there is little doubt that careful control of body temperature during and after surgery can markedly improve clinical outcomes.

Preventing, treating hypothermia
Heat may be transferred from the patient to the environment by four processes: conduction, convection, radiation and evaporation.

Passive methods of warming use the body's own heat as a source of thermal energy. Warmed blankets are only as effective as their source of heat and should be routinely replaced when they cool to ambient temperatures. Active warming provides a continual source of thermal heat regardless of the ambient temperature. See "Ways to Warm a Patient" on page 37 for examples of active heat sources.

Noteworthy newcomers include the Bair Paws Patient Adjustable Warming System (Arizant Healthcare) and the Cool/Heat OR Pad (Advanced Surfaces).

The Bair Paws gown is the first temperature-adjustable gown designed to be worn pre- and post-op. Unlike forced-air warming blankets that are laid over the patient, the Bair Paws gown is worn very much like a regular cotton gown. Patients can put it on upon admission, then when in pre-op, the gown can be attached to the warming unit (patients adjust the temperature of air that flows through the gown).

The Cool/Heat OR Pad warms the patient before, during and after surgery. When the weight of the patient compresses a viscoelastic foam pad lined with radiators, heat is emitted. Cool/Heat is designed with inherent temperature limits for patient safety; it can't get hot enough to burn the patient. "Our goal was to give nurses back time," says Ken Ellis, the president of Advanced Surfaces. "You turn it on and leave it alone. Nurses love it because of the simplicity. We're hoping to raise the level of hypothermia treatment."

A positive surgical experience
Beyond what we know about the science and the economics of patient warming, you can't discount the human touch. One of the most common complaints that patients express in the immediate post-op period is that of being cold. To some patients, feeling cold is worse than surgical pain.

"If there's one thing people seem to remember when they wake up from surgery is that they're very cold," says Tom Phlipot, the general manager of Progressive Dynamics Medical, which designs and manufactures a forced-air patient warming system called Life-Air 1000. "When active warming is used, patients have a much better recollection of overall surgical experience."